In certain types of ink jet printing systems, such as thermal ink jet (TIJ) printers, the maximum achievable operating frequency, F.sub.max, is inherently limited by: 1) the inability of the natural capillary action in the ink feed apparatus to adequately supply ink to the ink reservoir chamber (the ink cavity) of the printhead and 2) by oscillations of the ink meniscus at the orifice plate of the printhead which persist for some time, To, after drop ejection has occurred. One approach to extending F.sub.max as well as providing other operational improvements in thermal ink jet printheads is disclosed and claimed in copending Marzio A. Leban et al application Ser. No. 120,300 entitled "Integral Thin Film Injection System For Thermal Ink Jet Heads and Method of Operation", filed Nov. 13, 1987, now abandoned assigned to the present assignee and incorporated herein by reference.
Thermal ink jet printers having these operational characteristics are now generally well known in the art and are described, for example, in the Hewlett-Packard Journal, Volume 38, No. 5, May 1985, incorporated herein by reference. These printers employ printhead devices having resistive heater elements (resistors) which are normally aligned with corresponding ink ejection orifices in an adjacent orifice plate and are operative to receive electrical drive pulses from an external source. These pulses rapidly heat the heater resistors and thereby cause ink in an adjacent ink reservoir to vaporize and be forced out of the orifice plate during an ink jet printing operation. Thus, as the operating frequency of the printhead is extended out beyond a certain limit, there is a tendency for the natural capillary action of the ink feed system of the TIJ printer to inadequately supply the required volume of ink to the ink reservoirs associated with the heater resistors, the adjacent ink cavity and ink channel feeding the cavity.
This "ink starvation effect" becomes even more pronounced as the viscosity of the ink is increased. In many applications it is desirable to increase the ink viscosity in order to achieve an improved print quality on a variety of paper types and particularly plain paper. In addition to the above limitations imposed by this ink starvation effect, natural meniscus oscillations of the ink at the orifice further place a limitation on F.sub.max and persist for some time, To, immediately after a drop is ejected. During this time, To, further drop ejection is greatly restricted.